Automatically set Axis Option to least date using Gantt Chart

I'm trying to get a little creative using a Gantt chart to compare promotion averages. The chart will show where the user is compared to the average promotion rates - gantt style.

I have everything set up, the problem I'm running into is allowing the Axis Option to use the earliest date set by the user. In the attached sheet, I have a date of 1 Nov 02 in cell D30. However, if a earlier date is put in this cell the chart will not adjust accordingly. If I change the Axis Option to Auto, it completely throws the Gantt off. I have manually set the option to the corresponding date of 1 Nov 02 to make the chart work for this scenario. However not everyone that will use this will have a date of 1 Nov 02.

Is this doable? Or am I missing something so small it will make me face palm?

Any answer that fixes the issue will get + rep and a solved thread. Thanks in advance.